/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.asm.ClassReader;
import org.springframework.asm.ClassVisitor;
import org.springframework.asm.Label;
import org.springframework.asm.MethodVisitor;
import org.springframework.asm.Opcodes;
import org.springframework.asm.SpringAsmInfo;
import org.springframework.asm.Type;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Implementation of {@link ParameterNameDiscoverer} that uses the LocalVariableTable
 * information in the method attributes to discover parameter names. Returns
 * {@code null} if the class file was compiled without debug information.
 *
 * <p>Uses ObjectWeb's ASM library for analyzing class files. Each discoverer instance
 * caches the ASM discovered information for each introspected Class, in a thread-safe
 * manner. It is recommended to reuse ParameterNameDiscoverer instances as far as possible.
 *
 * @author Adrian Colyer
 * @author Costin Leau
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 2.0
 */
public class LocalVariableTableParameterNameDiscoverer implements ParameterNameDiscoverer
{

    private static final Log logger = LogFactory.getLog(LocalVariableTableParameterNameDiscoverer.class);

    // marker object for classes that do not have any debug info
    private static final Map<Member, String[]> NO_DEBUG_INFO_MAP = Collections.emptyMap();

    // the cache uses a nested index (value is a map) to keep the top level cache relatively small in size
    private final Map<Class<?>, Map<Member, String[]>> parameterNamesCache = new ConcurrentHashMap<>(32);


    @Override
    @Nullable
    public String[] getParameterNames(Method method)
    {
        Method                originalMethod = BridgeMethodResolver.findBridgedMethod(method);
        Class<?>              declaringClass = originalMethod.getDeclaringClass();
        Map<Member, String[]> map            = this.parameterNamesCache.get(declaringClass);
        if (map == null)
        {
            map = inspectClass(declaringClass);
            this.parameterNamesCache.put(declaringClass, map);
        }
        if (map != NO_DEBUG_INFO_MAP)
        {
            return map.get(originalMethod);
        }
        return null;
    }

    @Override
    @Nullable
    public String[] getParameterNames(Constructor<?> ctor)
    {
        Class<?>              declaringClass = ctor.getDeclaringClass();
        Map<Member, String[]> map            = this.parameterNamesCache.get(declaringClass);
        if (map == null)
        {
            map = inspectClass(declaringClass);
            this.parameterNamesCache.put(declaringClass, map);
        }
        if (map != NO_DEBUG_INFO_MAP)
        {
            return map.get(ctor);
        }
        return null;
    }

    /**
     * Inspects the target class. Exceptions will be logged and a maker map returned
     * to indicate the lack of debug information.
     */
    private Map<Member, String[]> inspectClass(Class<?> clazz)
    {
        InputStream is = clazz.getResourceAsStream(ClassUtils.getClassFileName(clazz));
        if (is == null)
        {
            // We couldn't load the class file, which is not fatal as it
            // simply means this method of discovering parameter names won't work.
            if (logger.isDebugEnabled())
            {
                logger.debug("Cannot find '.class' file for class [" + clazz + "] - unable to determine constructor/method parameter names");
            }
            return NO_DEBUG_INFO_MAP;
        }
        try
        {
            ClassReader           classReader = new ClassReader(is);
            Map<Member, String[]> map         = new ConcurrentHashMap<>(32);
            classReader.accept(new ParameterNameDiscoveringVisitor(clazz, map), 0);
            return map;
        }
        catch (IOException ex)
        {
            if (logger.isDebugEnabled())
            {
                logger.debug("Exception thrown while reading '.class' file for class [" + clazz + "] - unable to determine constructor/method parameter names",
                        ex);
            }
        }
        catch (IllegalArgumentException ex)
        {
            if (logger.isDebugEnabled())
            {
                logger.debug(
                        "ASM ClassReader failed to parse class file [" + clazz + "], probably due to a new Java class file version that isn't supported yet " + "- unable to determine constructor/method parameter names",
                        ex);
            }
        }
        finally
        {
            try
            {
                is.close();
            }
            catch (IOException ex)
            {
                // ignore
            }
        }
        return NO_DEBUG_INFO_MAP;
    }


    /**
     * Helper class that inspects all methods (constructor included) and then
     * attempts to find the parameter names for that member.
     */
    private static class ParameterNameDiscoveringVisitor extends ClassVisitor
    {

        private static final String STATIC_CLASS_INIT = "<clinit>";

        private final Class<?> clazz;

        private final Map<Member, String[]> memberMap;

        public ParameterNameDiscoveringVisitor(Class<?> clazz, Map<Member, String[]> memberMap)
        {
            super(SpringAsmInfo.ASM_VERSION);
            this.clazz = clazz;
            this.memberMap = memberMap;
        }

        private static boolean isSyntheticOrBridged(int access)
        {
            return (((access & Opcodes.ACC_SYNTHETIC) | (access & Opcodes.ACC_BRIDGE)) > 0);
        }

        private static boolean isStatic(int access)
        {
            return ((access & Opcodes.ACC_STATIC) > 0);
        }

        @Override
        @Nullable
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)
        {
            // exclude synthetic + bridged && static class initialization
            if (!isSyntheticOrBridged(access) && !STATIC_CLASS_INIT.equals(name))
            {
                return new LocalVariableTableVisitor(this.clazz, this.memberMap, name, desc, isStatic(access));
            }
            return null;
        }
    }


    private static class LocalVariableTableVisitor extends MethodVisitor
    {

        private static final String CONSTRUCTOR = "<init>";

        private final Class<?> clazz;

        private final Map<Member, String[]> memberMap;

        private final String name;

        private final Type[] args;

        private final String[] parameterNames;

        private final boolean isStatic;
        /*
         * The nth entry contains the slot index of the LVT table entry holding the
         * argument name for the nth parameter.
         */
        private final int[]   lvtSlotIndex;
        private       boolean hasLvtInfo = false;

        public LocalVariableTableVisitor(Class<?> clazz, Map<Member, String[]> map, String name, String desc, boolean isStatic)
        {
            super(SpringAsmInfo.ASM_VERSION);
            this.clazz = clazz;
            this.memberMap = map;
            this.name = name;
            this.args = Type.getArgumentTypes(desc);
            this.parameterNames = new String[this.args.length];
            this.isStatic = isStatic;
            this.lvtSlotIndex = computeLvtSlotIndices(isStatic, this.args);
        }

        private static int[] computeLvtSlotIndices(boolean isStatic, Type[] paramTypes)
        {
            int[] lvtIndex  = new int[paramTypes.length];
            int   nextIndex = (isStatic ? 0 : 1);
            for (int i = 0; i < paramTypes.length; i++)
            {
                lvtIndex[i] = nextIndex;
                if (isWideType(paramTypes[i]))
                {
                    nextIndex += 2;
                }
                else
                {
                    nextIndex++;
                }
            }
            return lvtIndex;
        }

        private static boolean isWideType(Type aType)
        {
            // float is not a wide type
            return (aType == Type.LONG_TYPE || aType == Type.DOUBLE_TYPE);
        }

        @Override
        public void visitLocalVariable(String name, String description, String signature, Label start, Label end, int index)
        {
            this.hasLvtInfo = true;
            for (int i = 0; i < this.lvtSlotIndex.length; i++)
            {
                if (this.lvtSlotIndex[i] == index)
                {
                    this.parameterNames[i] = name;
                }
            }
        }

        @Override
        public void visitEnd()
        {
            if (this.hasLvtInfo || (this.isStatic && this.parameterNames.length == 0))
            {
                // visitLocalVariable will never be called for static no args methods
                // which doesn't use any local variables.
                // This means that hasLvtInfo could be false for that kind of methods
                // even if the class has local variable info.
                this.memberMap.put(resolveMember(), this.parameterNames);
            }
        }

        private Member resolveMember()
        {
            ClassLoader loader   = this.clazz.getClassLoader();
            Class<?>[]  argTypes = new Class<?>[this.args.length];
            for (int i = 0; i < this.args.length; i++)
            {
                argTypes[i] = ClassUtils.resolveClassName(this.args[i].getClassName(), loader);
            }
            try
            {
                if (CONSTRUCTOR.equals(this.name))
                {
                    return this.clazz.getDeclaredConstructor(argTypes);
                }
                return this.clazz.getDeclaredMethod(this.name, argTypes);
            }
            catch (NoSuchMethodException ex)
            {
                throw new IllegalStateException("Method [" + this.name + "] was discovered in the .class file but cannot be resolved in the class object", ex);
            }
        }
    }

}
